Pollutants such as carbon monoxide, ozone, particulate matter, and other potentially harmful substances can be present in both indoor and outdoor air. Some cities and other municipal entities maintain air quality monitors to detect pollution levels. Reports of the air pollution levels measured by such monitors might be published in newspapers or on web sites, broadcast on television or radio, or otherwise be made known to the public. However, the monitors are typically present in only a limited number of locations and the air pollution levels measured in these locations do not necessarily represent the levels in other locations. Also, there may be some delay between the detection of an air pollutant and the announcement of the level of that pollutant. Changes could occur in a pollution level between the time a pollutant is detected and the time the level of that pollutant is published. Therefore, the pollution level a person is exposed to at a particular place and time could be significantly different from the published reports of air pollution levels.